The present application claims priority under 35 U.S.C. xc2xa7119 of Austrian Patent Application No. 586/2001, filed Apr. 11, 2001 the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a high-speed steel article which has high elevated-temperature strength and toughness and is produced by powder metallurgy by dispersing a liquid stream of an alloy with nitrogen into a metal powder and compacting the powder at high temperature under compression from all sides and optionally is hot worked thereafter.
2. Discussion of Background Information
High-performance high-speed steels include alloys with about 0.8 to 1.0% by weight of carbon, 14 to 18% by weight of tungsten, about 4.5% by weight of chromium, up to 2% by weight of molybdenum, at least 1.2 to 1.5% by weight of molybdenum, at least 1.2 to 1.5% by weight of vanadium, and 3 to 20% by weight of cobalt, the remainder being iron. The cause of the high performance that is achievable with these high-speed steels lies in the interaction of the strongly carbide-forming elements vanadium, tungsten, molybdenum and chromium, and the element cobalt, which acts through the basis mass or matrix. Along with tungsten and molybdenum, vanadium in particular is suited to provide the alloy with a high tempering resistance up to a temperature of about 600xc2x0 C. When high carbon content and high vanadium content are present at the same time, a large quantity of vanadium carbides is also formed, which results in a particularly high wear resistance of the material. For this reason, finishing tools in particular are made of high-speed steels that have elevated carbon and vanadium content. However, the limits of economical manufacturability through pyrometallurgical or casting methods with solidification in casting molds appear to be reached when an alloy with the chemical composition in percent by weight of 1.3 to 1.5 C, about 13 W, 4 Cr, 1 Mo, 8 to 12 Co and about 4.5 V, remainder iron, is used. Due to its high carbon content and its solidification structure even this material is workable only with difficulty and at a lowered, narrow forging temperature range and shows only low toughness values, in particular low impact bending strength, in the tempered state.
In order to be able to further increase the carbon content and the concentration of carbide-forming elements for increasing the carbide content and thus further increasing the wear resistance of the material on the one hand, while on the other hand achieving adequate workability and homogeneity of the article manufactured therefrom, powder metallurgy production of such alloyed parts is advantageous.
Powder metallurgy (PM) production essentially comprises atomization of a steel melt into metal powder, introduction and compression of the metal powder into a capsule, closing the capsule, and heating and hot isostatic pressing of the powder in the capsule into a dense, homogeneous material.
This PM material can be used to manufacture articles directly after an appropriate heat treatment, or can first be subjected to hot working, for example by forging.
Highly stressed high-speed steel articles, in particular cutting tools with a long service life, require a diverse property profile for an economic processing of parts.
The present invention provides a high-speed steel article, preferably for use in a high-performance cutting tool, which has a high degree of oxide purity and hence offers a low crack initiation potential and an increased degree of cutting edge sharpness, and possesses high hardness with commensurate toughness and high wear resistance in the tempered state of the material as well as improved hot hardness and elevated-temperature strength.
The present invention also provides a high-speed steel article suitable for use as a tool for the high-speed machining of materials without the use of lubricants, in particular for metal-cutting machining of light metals and corresponding alloys.
In accordance with the present invention there is provided a high-speed steel article of the aforementioned type which has a high degree of purity with a content and configuration of nonmetallic inclusions corresponding to a K0 value according to DIN 50 602, which is hereby fully incorporated herein by reference, of at most 3 and has the following chemical composition in percent by weight (as used in the present specification and the appended claims, all weight percentages are based on the total weight of the composition):
with a value of manganese minus sulfur (Mnxe2x88x92S) of at least 0.19, the remainder being iron and impurities related to the manufacturing process and accompanying elements, provided that the concentration ratio of tungsten and molybdenum (W/Mo) is between 5.2 and 6.5 and that the cobalt content is at most 70% of the value of (tungsten+molybdenum).
In one aspect of the steel article according to the invention, at least one or all of the following elements are present in the following concentration ranges in % by weight:
In another aspect, at least one or all of the following elements are present in the following concentration ranges in % by weight:
In yet another aspect, the article is a tool, e.g., a finishing tool, a cutting tool or a metal-cutting tool.
The present invention further provides a process for making a high-speed steel article by powder metallurgy, wherein the composition of the steel is as indicated above, including the various aspects thereof, said process comprising dispersing a liquid stream of the steel with nitrogen into a metal powder and compacting the powder at high temperature under compression from all sides (e.g., by hot isostatic pressing).
In one aspect, the process further comprises hot working of the compacted and compressed metal powder, e.g., by forging. In another aspect of the process, the article is a tool.
Furthermore, the present invention provides a process for the high-speed machining of material parts. The process comprises machining the material parts without lubricants with a powder metallurgy produced tool made of a high-speed steel. This steel has the composition indicated above.
According to one aspect of the process, the parts are made of metal, e.g., light metal or a corresponding alloy.